The bark on my well established lemon tree has started to split quite badly on the trunk and lower branches. Does anyone have any iteas what might be causing it and how to remedy it.

Thanks

I saw it happen once when the temp.dropped to below minus 10 .
Chopped of the worst affected areas in the Spring and it eventually recovered the following year.
Not sure where you are, but I've not heard of such low temps near the Costas of late so I presume its something else.

As you haven't received any further replies I googled it out of curiosity.
Apparently there are two common causes of the effects you describe.

One is exposure to hard frost as I mentioned, possibly minus 5 and below.
The other is sunburn believe it or not !
In both cases they are much more susceptible if heavy pruning has taken place leaving the lower branches and trunk exposed to extremes of temperature and direct sunlight.

Irregular watering can also add to the problem as I believe happened with mine when it received too much water just before a very cold snap.